This invention relates to a polyurethane elastomer possessing both high resilience and high clarity.
Polyurethane elastomers are well known. See, e.g., U.S. Pat. Nos. 4,294,951, 4,555,562 and 5,599,874. Polyurethane elastomers can be formed by reacting an isocyanate, e.g., diphenyl methane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, etc., with an organic polyol, e.g., polytetramethylene ether glycol, polyester diol, polyoxypropylene glycol, etc., and a chain extender, e.g., an aliphatic diol such as 1,4-butanediol. Additional components such as catalysts, surfactants and the like can also be added to the elastomer-forming reaction mixture in the usual amounts.
The reaction to form polyurethane elastomers can be a prepolymer process wherein an excess of an isocyanate is first reacted with an organic polyol to form an intermediate isocyanate-terminated prepolymer. The intermediate prepolymer is then contacted with a diol chain extender such as the aforementioned 1,4-butanediol, which reacts with the residual terminated isocyanate groups to form the polyurethane elastomer. Alternatively, a quasi-prepolymer or one-shot process may be employed. In the quasi-prepolymer process, a portion of the polyol is first reacted with the isocyanate to form a quasi-prepolymer. The remainder of the polyol and the diol chain extender are then reacted simultaneously with the quasi-prepolymer to form the polyurethane elastomer. In the one-shot process, all of the reactants are combined simultaneously to form the polyurethane elastomer.